As the coarse aggregate, the natural pumice in northern China was used. The lightweight aggregate concrete in which fiber contents are 1/100, 1/300, 1/500, 1/800, 1/1000 were used to test the compressive strength， peak load, elastic modulus, and the mechanical properties of fiber light weight aggregate concrete after freeze thaw in 3, 7, 14, 28, 90, and 180 days. Regulation for early strength and deformation and elastic modulus and freeze thaw cycles with fiber on light weight aggregate concrete was summarized and the influence of fiber to improve early strength and microstructure for different dosage of light weight aggregate concrete was investigated. The results show that fiber can strengthen the stability of the light weight aggregate concrete, improve its brittleness performance, and reduce the frost resistance at the most suitable proportion 1/1000. The fiber surface and the bonding situation of interface between fiber and slurry in the freeze thaw cycle process were observed under the microscopic view.